Variable focus optical devices

ABSTRACT

Variable focus optical devices, in particular lenses, can include a cavity at least partially defined by a flexible member ( 2 ), which may be retained between engaging portions of a frame member ( 8 ) and a ring member ( 12 ), such that a peripheral region of the membrane is caused to change direction more than twice. The engaging portions of the ring and frame may be high-friction surfaces. In addition, methods of filling a cavity of a lens with transparent fluid, methods of adjusting the pressure of fluid in the cavity, and methods of sealing such a cavity are described, as well the use of such lenses in adjustable spectacles.

The present invention relates to improvements in the field of variablefocus optical devices, in particular variable focus lenses, for exampleof the type in which the optical power of the lens is variable byvarying the volume and/or pressure of a transparent fluid within atransparent envelope.

Variable focus lenses are known and have been described for example inGB 2183059, GB 2184562 and WO96/38744. However, to date, despite themany examples of variable focus lenses described in the prior art, nonehave achieved widespread commercial acceptance as an alternative tofixed-focus ground glass or plastic lenses.

It is believed that the failure of known variable focus lenses to gaincommercial acceptance is due to a number of factors. For example, manyknown such lenses suffer from leakage of the fluid from the envelope inuse. Furthermore, many known such lenses suffer from poor opticalquality due to the mounting arrangement of the flexible membrane and/orthe material chosen for the membrane. A further contributor to the pooroptical quality of known lenses has been the fluid selected to fill theenvelope, which has had a less than optimal transparency or homogeneityof refractive index. An additional reason for the non-acceptance ofknown lenses has been their complex and bulky configuration which haslead to a poor aesthetic effect, for example when the known lenses havebeen mounted in spectacles, and has also increased the cost of suchspectacles to a level which is not competitive with traditionalfixed-focus lenses.

The present invention seeks to provide a variable focus lens and amethod of making a variable focus lens, embodiments of which overcome atleast some of the problems of known variable focus lenses, whereby amore commercially attractive product can be achieved. It also seeks toprovide eyewear incorporating variable focus lenses.

According to an invention disclosed herein, there is provided a variablefocus lens comprising a transparent envelope at least partially definedby a flexible, transparent membrane and containing a transparent fluid,a frame member engaging one face of the flexible membrane and a ringmember engaging an opposite face of the flexible membrane, the ringmember and the frame member being urged towards each other by retainingmeans, wherein the respective surfaces of the frame member and the ringmember that engage the flexible membrane are substantially complementaryand profiled so as to cause a peripheral region of the flexible membraneto change direction more than once.

It has been realised by the applicant that, in order to obtain a highoptical quality of the membrane, the membrane should be held undertension at all times. Furthermore, it has been found by the applicantthat the membrane, when under tension, and particularly when formed ofpreferred materials such as Mylar tends to form its own seal against theframe member or ring member.

The profiles of the engaging surfaces of the frame member and the ringmember allow the flexible membrane to be retained under tension on theframe member simply by the action of the engaging surfaces. In this waythe construction of the variable focus lens is considerably simplifiedin comparison to known such lenses.

The profiles of the engaging surfaces may be stepped or comprise one ormore projections and complementary recess(es). The portions of theengaging surfaces substantially perpendicular to the plane of theunstretched membrane will tend to frictionally engage the membrane asthe ring member is urged towards the frame member by the retainingmeans. Such frictional engagement will tend to stretch the membrane onthe frame member, ensuring that the membrane is under tension.

In a particularly advantageous arrangement, the engaging surfacescomprise at least one oblique surface which increases in radial extenttowards the frame member. In this way, as the ring member is urgedtowards the frame member by the retaining means, friction between theoblique surface of the ring member and the flexible membrane tends tourge the periphery of the membrane radially outwardly, therebyincreasing the tension in the membrane, i.e. stretching the membrane.

The ring member and frame member may be of a material or materials whichis/are sufficiently rigid to positively interengage with each other andto ensure that the ring member and frame member can maintain theflexible membrane under tension. The material of the ring member andframe member is preferably also lightweight to facilitate theincorporation of lenses described herein in spectacles. Thus, the ringmember and frame member may be made, for example, of a high impactresistant plastics material, or of aluminium, or of titanium.

It is generally advantageous to maximise the friction between theengaging surfaces and the membrane, not only to maximise the stretchingeffect described above, but also to ensure that the membrane is securelyheld by the ring member and the frame in the assembled lens. Preferablytherefore, at least one of the surfaces is a high friction surface.

This in itself is believed to be new and thus according to an inventiondisclosed herein there is provided a variable focus lens comprising atransparent envelope at least partially defined by a flexible,transparent membrane and containing a transparent fluid, a frame memberengaging one face of the flexible membrane and a ring member engaging anopposite face of the flexible membrane, the ring member and the framemember being urged towards each other by retaining means, wherein therespective surfaces of the frame member and the ring member that engagethe flexible membrane are substantially complementary and at least oneof the surfaces is a high friction surface.

For example, one or more of the frame member and the ring member may bemade of a material having a high coefficient of friction at its surface.Alternatively, at least one of the engaging surfaces may have beenroughened or expanded to increase its surface friction.

In a preferred arrangement, however, at least one of the engagingsurfaces is provided with a coating of high friction material. Aparticularly preferred material for this coating is rubber or asynthetic elastomer, as this has been found by the applicant to engagewell with the preferred materials for the membrane, such as Mylar.

A further advantage of providing at least one of the engaging surfaceswith a coating of rubber or synthetic elastomer is that the rubber orelastomer tends to form a high integrity fluid seal at the interfacebetween the engaging surface and the membrane.

Thus, according to an invention defined herein there is provided avariable focus lens comprising a transparent envelope at least partiallydefined by a flexible, transparent membrane and containing a transparentfluid, a frame member engaging one face of the flexible membrane and aring member engaging an opposite face of the flexible membrane, the ringmember and the frame member being urged towards each other by retainingmeans, wherein at least one of the engaging surfaces is provided with acoating of rubber or synthetic elastomer.

It has been found by the applicant that the coating need only be thin,in order to achieve an advantageous effect. For example, the coating mayhave thickness of less than 100 μm, or less than 50 μm, or less than 20μm or even less than 10 μm.

Preferably, the coating is provided on the engaging surface that engagesthe face of the membrane which also forms an inner surface of theenvelope, so that the sealing interface aids in the containment of thefluid. This surface will generally be provided on the frame member. Ofcourse, both engaging surfaces may be provided with a coating.

The peripheral shape of the ring member, and also of the frame member,may be chosen as required. For example, the members may have a circular,oval, elliptical, or other closed curve, peripheral shape.

The frame member may comprise a rigid transparent window forming a wallof the envelope. The rigid window may be of any suitable material, forexample glass, or a plastics material, such as polycarbonate. Indeed,for ease of manufacture, the frame member may be made entirely of suchtransparent material. Alternatively, the rigid window may form a part ofthe frame member, for example being bonded to and/or enclosed by anannular frame.

The frame member may be provided with a second engaging surface engaginga second membrane. In this case, a second ring member may be providedwith a second engaging surface for engaging the second membrane. Thesecond engaging surface may be opposed to the first engaging surface ofthe frame member. The second membrane may define a wall of the envelope.

Alternatively, the first ring member may be provided with a secondengaging surface engaging a second membrane. Again, a second ring membermay be provided with a second engaging surface for engaging the secondmembrane. The second engaging surface may be opposed to the firstengaging surface of the first ring member. The second membrane maydefine a wall of the envelope.

The first and second membranes may be formed from a single membrane web,although preferably the first and second membranes are discrete.

A duct may be provided through a wall of the envelope, preferable aradially outer wall, which duct is in communication with the envelope.Such a duct will allow fluid to be removed from or introduced to theenvelope in order that the volume and/or pressure of the fluid in theenvelope may be varied to vary the power of the lens.

The duct may be formed by a pre-formed bore, or drilled, in one or moreof the first or second ring members or the frame member.

The duct may be provided with suitable closure means to prevent leakageof fluid from the envelope through the duct. Such closure means may beas described in WO96/38744, or may be a rubber or elastomer bungpenetrable by a needle of a syringe and capable of self-sealing onremoval of the needle. Alternatively, a valve may be provided in theduct, arranged so that the duct is normally closed, but capable of beingopened by, for example, the needle of a syringe. In one embodiment, thevalve comprises a ball urged by a spring against an annular seat. Tovary the pressure of fluid in the envelope, a needle of a syringe orsimilar is inserted through the centre of the seat, thus displacing theball. Fluid can be then be introduced into or removed from the envelopeto vary the pressure therein. When the needle is retracted, the springurges the ball against the seat again to close the valve and seal theduct.

It has been found by the applicant that, with preferred transparentfluids such as silicone oil, which is relatively viscous, such a ductmust be relatively large in order to enable efficient filling of thelens. One way in which the effective size of such a duct may beincreased, is by providing a plurality of ducts in a wall of theenvelope.

This in itself is believed to be new, and thus according to an inventiondisclosed herein, there is provided a variable focus lens comprising atransparent envelope at least partially defined by a flexible,transparent membrane and containing a transparent fluid, and a pluralityof ducts provided in a wall of the envelope for introducing fluid intothe envelope.

The plurality of ducts may be provided with respective closure means,for example as described above, or may be provided with a single closuremeans for a plurality of ducts. The ducts may be distributed about theperiphery of the lens, but in a preferred arrangement the ducts areproximately grouped.

As an alternative to providing a plurality of ducts, it is possible toprovide a single duct having a large cross-section. It will beappreciated that the maximum width of the duct in the direction of theaxis of the lens is limited by the thickness of the wall of the envelopewhich forms the lens. However, the cross-sectional area of the duct canbe increased by forming the duct such that its width perpendicular tothe axis of the lens is greater than its width parallel to the axis ofthe lens.

The retaining means may be any suitable means, for example screws, clipsand the like. Respective retaining means may be provided for each ofsaid first and second ring members.

In a preferred arrangement, the retaining means take the form of adeformable portion of one of the frame member and the ring member,arranged to be deformed, for example crimped, over the other of theframe member and the ring member. In this case, the deformable portionmay be of metal, such as aluminium, stainless steel or titanium.

Advantageously, the retaining means may be provided by a pair ofspectacles or similar device, into which the lens is to be mounted.

The transparent fluid retained within the envelope may be any suitablefluid, for example silicone oil, such as 703 type silicone oil.

The fluid may be communicated to the envelope by means of a suitablepump, for example a syringe.

However, it has been realised by the applicant that a simple syringe isnot ideal as a pump for varying the focus of the lens. One reason forthis is that the plunger of the syringe is difficult to controlaccurately. For example, static friction between the piston and thesyringe barrel must be overcome before the plunger moves, such thatpressure applied to the plunger tends to build up until the staticfriction is overcome, at which point the plunger moves relativelyrapidly.

Thus, according to an invention disclosed herein, there is provided apump for a variable focus lens comprising a fluid chamber having anoutlet port and a linearly movable member arranged to vary the effectivevolume of the fluid chamber, wherein locating means are provided forlocating the movable member in a plurality of discrete positions.

In a simple arrangement the locating means may be in the form of twostops arranged to limit the movement of the movable member, for examplea piston or plunger, to a range having end points defined by respectivestops. The end points may correspond respectively to a firstpredetermined power of the lens, for example for the correction ofmyopia of a user, and a second predetermined power of the lens, forexample for correction of hypermetropia or presbyopia of a user. In thisway a bifocal lens may be produced which can be adjusted by the user forreading and close work or distance vision.

The stops may be variable in their positions, for example for initialsetting of two levels of power for the lens, and may be lockable in aselected position.

The locating means may comprise a series of locators, for example teethof a rack or the like, which may be engaged by a suitable mating member,in order that the movable member is adjustable step-wise.

It has also been found preferable by the applicant for users of variablefocus lenses, for example users of spectacles incorporating variablefocus lenses, to control the focus of the lenses by a rotationalmovement rather than a linear movement such as that of the piston of asyringe.

Thus, according to an invention disclosed herein, there is provided apump for a variable focus lens comprising a fluid chamber having anoutlet port and means for linearly varying the volume of the fluidchamber in response to a rotational movement of a control member.

The pump may comprise a pinion coupled for rotation with a control knoband engaging a rack coupled for linear movement to a piston provided inthe fluid chamber. Alternatively, a piston received within the fluidchamber may be provided on a threaded shaft, the shaft engaging with acomplementary threaded collar, such that the collar or the shaft may berotated to cause the piston to move linearly within the fluid chamber.Alternatively, the interior of the fluid chamber may be threaded, andthe periphery of the piston may be provided with a complementary threadsuch that rotation of the piston causes linear movement thereof withinthe fluid chamber.

In a presently preferred arrangement, a barrel member is provided havinga threaded exterior, circumferential wall, and a fluid port defined inan end wall thereof. The barrel member is received within a cap memberprovided with a complementary interior thread and an end wall opposed tothe end wall of the barrel member. The fluid chamber is defined by thevolume enclosed by the connected barrel and cap members. According tothis arrangement, as the cap member and barrel member are rotatedrelative to each other the cap moves away from or towards the end faceof the barrel member, thereby linearly increasing or reducing the volumeof the fluid chamber. The cap member may optionally be provided with apiston mounted in fixed relation to its end face and received within thebarrel member. In this case, the fluid chamber is defined between theend face of the barrel member and the piston, and relative rotation ofthe barrel member and cap member causes the piston to reduce theeffective volume of the fluid chamber.

Locating means as described above may be provided in the context of arotational control member.

According to an invention disclosed herein, there is provided a variablefocus lens in combination with a pump as described herein.

In a preferred arrangement, two variable focus lenses are provided in aspectacle frame. A single pump may be provided, although it is preferredfor a respective pump to be provided for each lens, so that each lens isindependently variable.

The pump(s) may be provided on the arms of the spectacle frames, forexample at the ends of the arms, so that they are hidden by the ears inuse.

Channels may be provided in the spectacle frame, for example in thearms, for fluid communication between the lenses and the pump(s).

The pump(s) may be arranged to be detachable from the spectacles, forexample permanently detachable after an initial setting operation of thefocus of the lenses. The pump(s) may be arranged to be detachable fromthe spectacles such that when the pump(s) is/are detached the fluidcommunication channels are automatically closed off, for example bymeans of a valve.

In a preferred embodiment, a pair of spectacles has two pumps, one foreach lens, with each pump being removably attached to an arm of thespectacles. Fluid communication between each pump and its respectivelens is achieved by means of flexible tubing extending from the pump tothe lens. The flexible tubing is received in a channel in the frame ofthe spectacles for at least part of its length. When the user has setthe focus of the lens, the tubing is closed and cut, and the pump andthe portion of the tubing attached thereto is detached and discarded.

In one particularly preferred form, a part of the tubing connecting thelens and the pump is received in a channel formed in the main frame ofthe spectacles, preferably in the side facing the user. The tubingprojects from this recess beyond the side of the spectacles to join thepump attached to the arm of the spectacles.

The tubing can be closed in any suitable manner. However, it ispreferred for the tubing to be clamped closed, for example by means of ascrew urging the sides of the tubing together. In a preferred form, ascrew is provided in a passage in the frame of the spectacles,perpendicular to and intersecting the channel in which the tubing isreceived. On the opposite side of the channel from the screw is a memberwhich extends across the channel in the form of a bridge. When it isdesired to close the tubing, the screw is screwed into the passage, andthe end of the screw compresses the tubing against the member to closeit. The part of the tubing which projects beyond the end of the channelcan then be removed, for example by cutting it so that its end liesflush with the side of the frame.

In a particularly preferred embodiment, the member is formed by a partof the hinge attaching the arm to the main frame. This helps to retainthe tubing in the channel, and avoids the need to provide a separatemember.

As an alternative, the tubing could be closed by compression means otherthan a screw. For example, the frame may be provided with a button,which when depressed compresses the tubing against a member to close it.The button Way be arranged such that it latches when it is depressed, toensure that the tubing remains closed. In addition, the button can beprovided with means for retaining it in its original position, toprevent accidental operation. These means may take the form of aprotuberance on the button, which fits into a corresponding recess inthe frame.

In addition, means can be provided in the spectacles to allow the tubingto be cut. For example, a button carrying a blade may be provided, theblade severing the tubing when the button is depressed. This button maybe provided separately; however, it is preferred that the button whichcloses the tubing and the button which cuts it are combined, so that thetubing can be closed and cut in a single movement. This simplifies theprocess of setting the spectacles to a desired focus.

As mentioned in WO96/38744, the lenses can be pre-filled with fluidduring their manufacture. The pumps then need only contain a sufficientamount of fluid to allow the adjustment of the focus of the lenses.

It will be appreciated that it is very important for the lens to becompletely filled with fluid, with no air bubbles in the lens. Thepresence of air bubbles is extremely distracting for the wearer of thespectacles.

A number of approaches can be taken to filling the lens so as to avoidthe presence of air bubbles in the filled lens. For example, in onemethod which has proved effective, some of the air in the envelope ofthe lens is first sucked out, and then a similar amount of fluid isinjected. The cycle of air removal followed by fluid injection is thenrepeated as necessary until the lens is filled with fluid.

In an alternative method, a needle whose external diameter is less thanthe internal diameter of the duct is used to inject the fluid. The gapbetween the needle and the needle allows air in the lens to escape asfluid is injected. Fluid can still be injected through the needle whileit is being withdrawn from the duct.

It is also preferred for the fluid used to fill the lens to be degassedprior to filling, to reduce the chance of bubbles forming in the lensafter filling.

Filling the lens will normally involve injection of a relatively viscousfluid through a narrow passageway. The filling process can befacilitated by heating the fluid prior to injection, so as to reduce itsviscosity.

The variable focus lens described herein may be provided with at leastone transparent, protective cover for the or each flexible membrane. Thecover may be, for example, a rigid sheet of transparent material, forexample glass or a plastics material such as polycarbonate. Theprotective cover may be mounted, for example bonded, to the ring memberor the frame member.

As mentioned above it has been found by the applicant that in order toobtain a desired optical quality of a variable focus lens it isimportant that the membrane is maintained under tension. For thispurpose it is advantageous to form the membrane from a heat-shrinkableplastics material.

Thus, according to an invention disclosed herein, there is provided amethod of making a variable focus lens having a flexible, transparentmembrane supported in a frame, wherein the membrane is heat treatedwhile held in the frame to increase the tension in the membrane.

It has been found by the applicant that, at least with preferredmaterials for the membrane, e.g. Mylar, heat treatment of the membranecauses the membrane material to contract and thereby increase thetension in the membrane.

The membrane may be treated using any suitable source of heat, and in apreferred arrangement the heat is provided by a source of hot air, suchas a hair dryer, a hot air gun or a fan heater.

According to an invention disclosed herein, there is provided a methodof making a variable focus lens having a flexible, transparent membranesupported in a frame, wherein the membrane is pre-tensioned, and theframe is mounted to the membrane while the membrane is pre-tensioned. Inthis way, a convenient method of ensuring that the membrane is intension on the frame is provided.

Any suitable means may be provided for pre-tensioning the membrane. Forexample, the principles for tensioning the membrane disclosed in GB2184562 and 2183059 may be applied in this novel way to thepre-tensioning of the membrane.

The frame may be a frame as disclosed elsewhere herein.

The variable focus lens described above is of course suitable for use inspectacles. However, it can also be used on any form of eyewear where itmay be desired to incorporate corrective optics, including but notlimited to sunglasses, swimming goggles, skiing goggles, squash glasses,sports eyewear in general, welding masks, welding goggles, laboratorygoggles, and protective eyewear in general. The lens may be provided asan insert, or may have means for attachment to the outside of theeyewear.

If the lens is to be used in sunglasses, then the material of themembranes or the fluid itself could be tinted. Further, it is possibleto use metallized Mylar, which reflects a portion of the light incidentthereon and transmits the remainder, as the material of the outermembrane, thereby providing reflective sunglasses.

A variable focus lens and spectacles embodying many of the advantageousfeatures described herein and to which the other features describedherein may be applied will now be described in detail, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 shows an axial section of a portion of a variable focus lensduring construction thereof;

FIG. 2 shows a section similar to that of FIG. 1 but showing thecompleted lens.

FIG. 3 is a partial sectional view of a variable focus lens;

FIG. 4 is a sectional view of a pump for a variable focus lens;

FIG. 5 is a sectional view of another pump for a variable focus lens;

FIG. 6 is a sectional view of another pump for a variable focus lens;

FIG. 7 is a perspective view of part of a pair of spectacles;

FIG. 8 is an enlarged view of a part of the spectacles;

FIG. 9 is a sectional view of part of the spectacles; and

FIG. 10 is a sectional view of part of an alternative pair ofspectacles.

The lens described and illustrated herein may be utilised in an opticalapparatus constructed and arranged to be adjusted as described andclaimed in WO96/38744.

The lens shown in FIG. 2 comprises first and second transparent,flexible membranes 2 which are tensioned and which define therebetweenan envelope 30 in which a transparent fluid 4, such as silicone oil, iscontained. In the embodiment illustrated the membranes 2 are of Mylar,for example, 23 μm Type D Mylar.

The membranes 2 are held in tension by a support 6. The support 6defines the periphery of the lens, and of the envelope 30, and isarranged to hold the flexible membranes 2 under tension. The support 6is also arranged to seal the lens.

As can be seen from FIG. 1, the support 6 is formed by interengaging aframe member 8 and first and second ring members 10,12 of aluminum. Inthis respect, the frame member 8 has a radially extending flange 14which is stepped as indicated at 16. The frame member 8 also has anaxially extending rim 18. The first ring member 10 has a radiallyoutwardly projecting portion 20 defining a first step 22 whichcooperates with the step 16 of the frame member 8 and a second step 24which cooperates with a step 26 of the second ring member 12. The secondring member 12 has a recess 28 arranged radially outwardly therein.

Where the completed lens is to have a generally circular periphery, forexample, a first membrane 2, which is circular, is positioned to extendwithin the frame member 8 such that its periphery extends along theradial flange 14 thereof. The first ring member 10 is then supportedwithin the frame member 8 such that the complementary steps 16 and 22thereof interengage. This interengagement positions the first ringmember 10 relative to the frame member 8. The interengagement also bendsthe peripheral circumference of the first membrane 2 through twodifferent directions as is clearly shown in FIG. 1.

A second circular membrane 2 is then positioned across the frame member8 such that its periphery extends along the upper radially extendingsurface of the first ring member 10. Thereafter, the second ring member12 is positioned such that the steps 24 and 26 of the first and secondring members 10,12 cooperate to retain the second ring member 12 inposition within the frame member 8, and to bend the periphery of thesecond membrane 2 through two directions. The tolerances of the members8,10,12 are chosen such that even when the arrangement is in theinterengaged position shown in FIG. 1, the two membranes 2 are firmlyheld by the interengaged members.

The construction has the considerable advantage that the circularmembranes 2 do not have to be produced to close tolerances. Eachcircular membrane 2 can be cut to be generally circular and to have adiameter which is somewhat larger than is required. In its turn, eachmembrane 2 is positioned as described above and held by theinterengagement of the corresponding ring members 10, 12. Any excessmaterial of the membrane 2 can then be trimmed simply using a knife withthe ring members 10,12 acting as guides.

To complete the construction of the lens it is necessary to ensure thatthe frame member and the first and second ring members 8,10,12 aresecured together such that the peripheries of the membranes 2 are firmlyretained to seal the lens and to prevent any leakage from the envelope30 defined between the two membranes 2. In the embodiment illustrated,the retention of the membranes 2 is achieved by crimping and deformingthe frame member 8. In this respect, the upstanding, axially extending,free end of the limb 18 of the frame member 8 is bent over to bereceived within the recess 28 of the second ring member 12. Any excessmaterial deformed from the ring 8 during this crimping operation isreceived within an annular space 32 which is defined between theradially outward peripheries of the first and second ring members 10 and12, and the inner periphery of the limb 18 of the frame member 8.

Once the lens has been constructed, as shown in FIG. 1, and with theframe member 8 deformed to secure the structure, a duct 34 is drilledthrough the frame 6 into the envelope 30. The envelope 30 can then befilled with the transparent fluid 4 through the duct 34. With 703silicone oil as the fluid, the resultant lens achieves a focal lengthrange of at least −6 to +10 dioptres, and the range −10 to +10 dioptresshould be achievable. Of course, it will be appreciated that, in analternative embodiment, the rings are formed with ducts before they areassembled.

Fluid may be introduced into the envelope 30 by way of the duct 34 andretained therein by use, for example, of ducts, plugs and sealing meansas described in WO96/38744. In an embodiment, the lens is pre-filled atthis stage with the fluid 4 and an appropriate material is provided inthe duct 34 to seal the envelope 30. However, the material sealing theduct 34 is preferably penetrable by a syringe, for example, so that thepressure of the fluid 4 within the envelope 30 can be adjusted. As analternative, a self-sealing valve could be positioned in the duct, asdescribed above.

In the embodiment shown, the two axially outer surfaces of the lens areeach protected by a sheet 36 of a polycarbonate. Each polycarbonatesheet 36, for example, may be about ½ millimetre thick. It will beappreciated that these sheets 36 are arranged to extend substantiallyparallel to each other. The circumferential periphery of each of thesheets 36 may be fixed to the annular frame 6 in any appropriate manner.For example, the sheets 36 may be adhered to the frame 6. Additionallyand/or alternatively, a plastics material frame (not shown) of a pair ofspectacles, for example, may be arranged to receive the annular frame 6in a manner to retain the sheets 36 against the annular frame 6 in theposition of FIG. 2.

FIG. 3 shows a fluid-filled lens according to a different arrangement.In this case there is only a single ring member 12 which has an obliqueengaging surface 38 complimentary to the oblique engaging surface 40 ofthe frame member 8. A single flexible membrane 2 is held between theseengaging surfaces 38,40, which are urged together by retaining means inthe form of a crimped limb 18 of the frame member 8. A wall of theenvelope containing the transparent fluid 4 is provided by apolycarbonate window 42 received by the annular part 44 of the framemember 8.

FIG. 4 shows a pump for a variable focus lens in the form of a modifiedsyringe having a barrel 45 and a piston 48 mounted on a piston rod 50.The piston rod 50 is provided along one side with a rack of teeth. Acollar 52 is clipped to the rim of the barrel 46 and the shaft 50 passesthrough a central aperture defined in the collar. A tooth of the collarprojects into the aperture and engages the teeth of the shaft 50, suchthat the shaft 50, and hence the piston 48, is movable step-wise througha series of discrete locations defined by the teeth of the shaft 50.

Stops 56 are clipped to the shaft 50 and have complementary teeth whichengage the teeth of the shaft 50 and maintain the stops 56 in positionrelative to the shaft. The stops 56 engage the collar 52 when the shaft50 is at either end of the range of movement defined by the stops 56.

FIG. 5 shows another pump for a variable focus lens. The pump comprisesa cylindrical barrel 58 with a threaded exterior and cap 60 with acomplementary threaded interior engaging the thread of the barrel 58.Between the barrel and the cap is defined a fluid chamber 62. As thebarrel and cap are rotated relative to each other the effective volumeof the fluid chamber 62 is varied so that fluid can be forced out of orsucked through a fluid port 64 defined in an end face of the barrel 58.

FIG. 6 shows a further pump use with a variable focus lens. Again, thispump is in the form of a modified syringe, having a barrel 70 and apiston 72 mounted on a piston rod 74, which has a rack. 76 of teeth onone side. Passing through the barrel is an axle 78, on which a piniongear 80 is mounted. The pinion 80 meshes with the rack 76. Attached toan end of the axle, which projects beyond the barrel, is a wheel 82(partly shown in phantom), which can be rotated by a user. Rotation ofthe wheel 820 in turn rotates the pinion 80, which drives the rack 76and thus moves the piston 72 in the barrel 70. Fluid can thus be forcedout of and sucked into the barrel, to vary the pressure in the lens,simply by rotating the wheel. Of course, other forms of gearing can beused to link the wheel to the piston rod.

FIG. 7 shows a part of a pair of spectacles 100 employing two variablefocus lenses. As will be seen, one of the lenses 102 is connected to apump 104, removably attached to an arm 106 of the spectacles, by alength of tubing 108. The other lens is also provided with a pump in ananalogous manner. The pumps can be of the form described above, althoughit will be appreciated that any suitable form of pump can be used.

The area of attachment between the main frame 110 of the spectacles andthe arm 106 is shown in more detail in FIG. 8. It will be seen that thetubing 108 extends from the lens through a channel 112 formed in theframe 110 and open towards the rear (ie the side facing the wearer)thereof. Part of the hinge (shown schematically as 114) is fixed toeither side of the channel, and extends across it in the manner of abridge.

The frame also includes a threaded passage 116, as shown in FIG. 9,which accommodates a screw 118. The threaded passage 116 opens into thechannel 112, and is aligned with the part 114 of the hinge which bridgesthe channel.

In use, the pressure inside the lens, and thus its focus, is adjusted bymeans of the pump 104. When the desired focus has been achieved, thescrew 118 is screwed into the passage 116 to close the tubing 108. Inparticular, the end of the screw 118 clamps the tubing 108 against thepart 114 of the hinge which bridges the channel. The screw is preferablyscrewed in and out by means of an Allen key, although of course any formof screw may be used.

Once the tubing 108 is clamped closed, the pump 104 is detached from thearm 106 of the spectacles, and the tubing is cut as indicated at 120,flush with the edge of the frame 110. The same process is repeated forthe other lens.

An alternative arrangement for closing and cutting the tubing 108 isshown in FIG. 10. Here, the tubing is closed by means of a projection122 attached to a button 124, which slides in an opening in the frame.When the button 124 is depressed, the projection 122 presses the tubingagainst the part 114 of the hinge of the spectacles, thus closing it.The button can be provided with means to latch it in its closedposition, as shown at 126 and 128. The button can also be provided withmeans (not shown) to retain it in its original position until it ispressed.

In addition, the button 124 can be provided with a blade 130 for cuttingthe tubing. The blade 130 and tubing 108 are arranged such that theblade only cuts the tubing after the tubing has been closed by theprojection 122. A single depression of the button thus serves to closethe tubing and cut it.

The button 124 has been shown in the front face of the frame 110 of thespectacles. However, it will be appreciated that it could also bearranged in the top face of the frame of the spectacles. The memberwould then bear against a side wall of the channel 112 to close thetubing.

The features described herein may be used either separately or in anysuitable combination. It will be appreciated that alterations andmodifications may be made to the embodiments described and illustratedherein within the scope of this application.

For example, although the much mention has been made herein of variablefocus lenses, the advantageous features described herein may also beapplied to other optical devices. For example, by providing a suitablesilvered surface in the lens described herein, a mirror of variablefocus may be manufactured in accordance with the present disclosure. Thesilvered surface may be applied to the flexible membrane, or may beapplied to a rigid surface viewed through the flexible membrane. Ofcourse, in the case of a silvered flexible membrane, it is not necessaryfor the fluid within the envelope to be transparent, as light is notrequired to pass through it in use. Indeed, the optical properties ofthe fluid in this case are irrelevant and the fluid may be opaque.

1. A variable focus lens comprising a transparent envelope at leastpartially defined by a flexible, transparent membrane and containing atransparent fluid, a frame member engaging one face of the flexiblemembrane and a ring member engaging an opposite face of the flexiblemembrane, the ring member and the frame member being urged towards eachother by retaining means, wherein the respective surfaces of the framemember and the ring member that engage the flexible membrane aresubstantially complementary and profiled so as to cause a peripheralregion of the flexible membrane to change direction more than once.
 2. Avariable focus lens as claimed in claim 1, wherein the profiles of theengaging surfaces are stepped.
 3. A variable focus lens as claimed inclaim 1, wherein the profiles of the engaging surfaces comprise one ormore projections and complementary recess(es).
 4. A variable focus lensas claimed in claim 1, wherein the ring member and frame member are. ofa material or materials which is/are sufficiently rigid to positivelyinterengage with each other and to ensure that the ring member and framemember can maintain the flexible membrane under tension.
 5. A variablefocus lens as claimed in claim 4, wherein the material of the ringmember and frame member is also lightweight.
 6. A variable focus lens asclaimed in claim 5, wherein the ring member and frame member are made ofa high impact resistant plastics material.
 7. A variable focus lens asclaimed in claim 6, wherein the ring member and frame member are made ofaluminium.
 8. A variable focus lens as claimed in claim 6, wherein thering member and frame member are made of titanium.
 9. A variable focuslens as claimed in claim 1, wherein at least one of the surfaces is ahigh friction surface.
 10. A variable focus lens comprising atransparent envelope at least partially defined by a flexible,transparent membrane and containing a transparent fluid, a frame memberengaging one face of the flexible membrane and a ring member engaging anopposite face of the flexible membrane, the ring member and the framemember being urged towards each others by retaining means, wherein therespective surfaces of the frame member and the ring member that engagethe flexible membrane are substantially complementary and at least oneof the surfaces is a high friction surface.
 11. A variable focus lens asclaimed in claim 9, wherein one or more of the frame member and the ringmember is made of a material having a high coefficient of friction atits surface.
 12. A variable focus lens as claimed in claim 1, whereinthe ring member and the frame member have a circular, oval, elliptical,or other closed curve, peripheral shape.
 13. A variable focus lens asclaimed in claim 1, wherein the frame uieiuber comprises a rigidtransparent window forming a wall of the envelope.
 14. A variable focuslens as claimed in claim 13, wherein the rigid window is of a suitablematerial, such as glass or a plastics material such as polycarbonate.15. A variable focus lens as claimed in claim 14, wherein the framemember is made entirely of such transparent material.
 16. A variablefocus lens as claimed in claim 13, wherein the rigid window forms a partof the frame member, for example being bonded to and/or enclosed by anannular frame.
 17. A variable focus lens as claimed in claim 1, whereinthe frame member is provided with a second engaging surface engaging asecond membrane.
 18. A variable focus lens as claimed in claim 17,wherein a second ring member is provided with a second engaging surfacefor engaging the second membrane.
 19. A variable focus lens as claimedin claim 17, wherein the second engaging surface is opposed to the firstengaging surface of the frame member.
 20. A variable focus lens asclaimed in claim 17, wherein the second membrane defines a wall of theenvelope.
 21. A variable focus lens as claimed in claim 1, wherein thefirst ring member is provided with a second engaging surface engaging asecond membrane.
 22. A variable focus lens as claimed in claim 21,wherein a second ring member is provided with a second engagiuy surfacefor engaging the second membrane.
 23. A variable focus lens as claimedin claim 20, wherein the second engaging surface is opposed to the firstengaging surface of the first ring member.
 24. A variable focus lens asclaimed in claim 21, wherein the second membrane defines a wall of theenvelope.
 25. A variable focus lens as claimed in claim 17, wherein thefirst and second membranes are formed from a single membrane web.
 26. Avariable focus lens as claimed in claim 17, wherein the first and secondmembranes are discrete.
 27. A variable focus lens as claimed in claim 1,wherein a duct is provided through a wall of the envelope, which duct isin communication with the envelope.
 28. A variable focus lens as claimedin claim 27, wherein said wall is a radially outer wall.
 29. A variablefocus lens as claimed in claim 26, wherein said duct is formed by apre-formed bore in one or more of the first or second ring members orthe frame member.
 30. A variable focus lens as claimed in claim 26,wherein said duct is drilled in one or more of the first or second ringmembers or the frame member.
 31. A variable focus lens as claimed inclaim 27, wherein the duct is provided with suitable closure means toprevent leakdye of fluid from the envelope through the duct.
 32. Avariable focus lens as claimed in claim 31, wherein said closure meanstake the form of a rubber or elastomer bung penetrable by a needle of asyringe and capable of self-sealing on removal of the needle.
 33. Avariable focus lens as claimed in claim 31, wherein a valve is providedin the duct, arranged so that the duct is normally closed, but capableof being opened by, for example, the needle of a syringe.
 34. A variablefocus lens as claimed in claim 33, wherein said valve comprises a ballurged by a spring against an annular seat.
 35. A variable focus lens asclaimed in claim 27, wherein a plurality of ducts are provided in a wallof the envelope.
 36. A variable focus lens comprising a transparentenvelope at least partially defined by a flexible, transparent membraneand containing a transparent fluid, and a plurality of ducts provided ina wall of the envelope for introducing fluid into the envelope.
 37. Avariable focus lens as claimed in claim 35, wherein the plurality ofducts are provided with respective closure means.
 38. A variable focuslens as claimed in claim 35, wherein the plurality of ducts are providedwith a single closure means.
 39. A variable focus lens as claimed inclaim 35, wherein the ducts are proximately grouped.
 40. A variablefocus lens as claimed in claim 27, wherein a single duct having a largecross-section is provided.
 41. A variable focus lens as claimed in claim40, wherein the cross-sectional area of the duct is increased by formingthe duct such that its width perpendicular to the axis of the lens isgreater than its width parallel to the axis of the lens.
 42. A variablefocus lens as claimed in claim.18, wherein respective retaining meansare provided for each of said first and second ring members.
 43. Avariable focus lens as claimed in claim 1, dependent thereon, whereinthe retaining means take the form of a deformable portion of one of theframe member and the ring member, arranged to be deformed, for examplecrimped, over the other of the frame member and the ring member.
 44. Avariable focus-lens as claimed in claim 43, wherein the deformableportion is of metal, such as aluminium, stainless steel or titanium. 45.A variable focus lens as claimed in claim 1, wherein said transparentfluid retained within the envelope is silicone oil, such as 703 typesilicone oil.
 46. A variable focus lens as claimed in claim 1, whereinthe fluid is communicated to the envelope by means of a suitable pump,for example a syringe.
 47. A pump for a variable focus lens comprising afluid chamber having an outlet port and a linearly movable memberarranged to vary the effective volume of the fluid chamber, whereinlocating means are provided for locating the movable member in aplurality of discrete positions.
 48. A pump as claimed in claim 47,wherein said locating means are in the form of two stops arranged tolimit the movement of the movable member, for example a piston orplunger, to a range having end points defined by respective stops.
 49. Apump as claimed in claim 48, wherein the stops are variable in theirpositions.
 50. A pump as claimed in claim 49, wherein the stops arelockable in a selected position.
 51. A pump as claimed in claim 47,wherein the locating means comprises a series of locators which may beengaged by a suitable mating member, in order that the movable member isadjustable step-wise.
 52. A pump as claimed in claim 51, wherein saidseries of locators are in the form of the teeth of a rack or the like.53. A pump for a variable focus lens comprising a fluid chamber havingan outlet port and means for linearly varying the volume of the fluidchamber in response to a rotational movement of a control member.
 54. Apump as claimed in claim 53, wherein said pump comprises a pinioncoupled for rotation with a control knob and engaging a rack coupled forlinear movement to a piston provided in the fluid chamber.
 55. A pump asclaimed in claim 53, wherein a piston received within the fluid chamberis provided on a threaded shaft, the shaft engaging with a complementarythreaded collar, such that the collar or the shaft may be rotated tocause the piston to move linearly within the fluid chamber.
 56. A pumpas claimed in claim 53, wherein the interior of the fluid chamber isthreaded, and the periphery of the piston is provided with acomplementary thread such that rotation of the piston causes linearmovement thereof with in the fluid chamber.
 57. A pump as claimed inclaim 53, comprising a barrel member with a threaded exterior, acircumferential wall, and a fluid port defined in an end wall thereof,which barrel member is received within a cap member provided with acomplementary interior thread and an end wall opposed to the end wall ofthe barrel member, said fluid chamber being defined by the volumeenclosed by the connected barrel and cap members.
 58. A pump as claimedin claim 57, wherein said cap member is provided with a piston mountedin fixed relation to its end face and received within the barrel member,such that the fluid chamber is defined between the end face of thebarrel member and the piston, and relative rotation of the barrel memberand cap member causes the piston to reduce the effective volume of thefluid chamber.
 59. A pump as claimed in claim 53, wherein locating meansfor locating the movable member in a plurality of discrete positions.60. A variable focus lens in combination with a pump as claimed in claim47.
 61. Eyewear in which two variable focus lenses as claimed in claim60 are provided in a spectacle frame.
 62. Eyewear as claimed in claim61, wherein a single pump is provided.
 63. Eyewear as claimed in claim61, wherein a respective pump is provided for each lens, so that eachlens is independently variable.
 64. Eyewear as claimed in claim 61,wherein the pumps are provided on the arms of the spectacle frames, forexample at the ends of the arms, so that they are hidden by the ears inuse.
 65. Eyewear as claimed in claim 61, wherein channels are beprovided in the spectacle frame, for example in the arms, for fluidcommunication between the lenses and the pump(s).
 66. Eyewear as claimedin claim 61, wherein the pump(s) are arranged to be detachable from thespectacles after an initial setting operation of the focus of thelenses.
 67. Eyewear as claimed in claim 66, wherein the pump(s) arepermanently detachable.
 68. Eyewear as claimed in claim 66, wherein thepump(s) are arranged to be detachable from the spectacles such that whenthe pump(s) is/are detached the fluid communication channels areautomatically closed off.
 69. Eyewear as claimed in claim 68, whereinsaid channels are automatically closed off by means of a valve. 70.Eyewear as claimed in claim 63, comprising a pair of spectacles with twopumps, one for each lens, each pump being removably attached to an armof the spectacles, wherein fluid communication between each pump and itsrespective lens is achieved by means of flexible tubing extending fromthe pump to the lens, the tubing being received in a channel in theframe of the spectacles for at least a part of its length, the tubingbeing closed and cut after a user has set the focus of the lens, and thepump and the attached portion of tubing then being detached anddiscarded.
 71. Eyewear as claimed in claim 70, wherein a part of thetubing connecting the lens and the pump is received in a channel formedin the main frame of the spectacles.
 72. Eyewear as claimed in claim 71,wherein said channel is in the side of the main frame facing the user.73. Eyewear as claimed in claim 70, wherein the tubing is closed bybeing clamped closed.
 74. Eyewear as claimed in claim 73, wherein saidtubing is clamped closed by means of a screw urging the sides of thetubing together.
 75. Eyewear as claimed in claim 74, wherein a screw isprovided in a passage in the frame of the spectacles, perpendicular toand intersecting the channel in which the tubing is received, wherein amember is provided on the side of the channel opposite the screwextending across the channel in the form of a bridge, and wherein thescrew may be screwed into the passage to compress the tubing against themember to close it.
 76. Eyewear as claimed in claim 75, wherein themember is formed by a part of the hinge attaching the arm of thespectacles to the main frame.
 77. Eyewear as claimed in claim 73,wherein the tubing is clamped closed by means of a button which, whendepressed, compresses the tubing against a member to close it. 78.Eyewear as claimed in claim 77, wherein said button is arranged to latchwhen it is depressed, to ensure that the tubing remains closed. 79.Eyewear as claimed in claim 76, wherein said button is provided withmeans for retaining it in its original position, to prevent accidentaloperation.
 80. Eyewear as claimed in claim 79, wherein said means takethe form of a protuberance on the button, which fits into acorresponding recess in the frame.
 81. Eyewear as claimed in claim 70,wherein means are provided in the spectacles to allow the tubing to becut.
 82. Eyewear as claimed in claim 81, wherein a button carrying ablade is provided, the blade severing the tubing when the button isdepressed.
 83. Eyewear as claimed in claim 82, wherein the button whichcloses the tubing and the button which cuts it are combined, so that thetubing can be closed and cut in a single movement.
 84. A method offilling an envelope of a variable focus lens with transparent fluid,including tha steps of sucking out some of the air in the envelope,injecting a similar amount of fluid into the envelope, and repeating thecycle of air removal followed by fluid injection until the envelope isfilled with fluid.
 85. A method of filling an envelope of a variablefocus lens with transparent fluid, in which a needle is used to injectfluid into the envelope through a duct, wherein the external diameter ofthe needle is smaller than the internal diameter of the duct, such thatair in the envelope can escape as fluid is injected.
 86. A method offilling an envelope of a variable focus lenss with transparent fluid,wherein the fluid used to, fill the envelope is degassed prior tofilling.
 87. A method of filling an envelope of a variable focus lenswith transparent fluid, in which the fluid is heated prior to filling,to reduce its viscosity.
 88. A variable focus lens as claimed in claim1, wherein said lens is provided with at least one transparent,protective cover for the or each flexible membrane.
 89. A variable focuslens as claimed in claim 88 wherein the cover is a rigid sheet oftransparent material.
 90. A variable focus lens as claimed in claim 89,wherein said material is glass or a plastics such as polycarbonate. 91.A variable focus lens as claimed claim 1, wherein the or each flexiblemembrane is formed from a heat-shrinkable plastics material.
 92. Amethod of making a variable focus lens having a flexible, transparentmembrane supported in a frame, wherein the membrane is heat treatedwhile held in the frame to increase the tension in the membrane.
 93. Amethod as claimed in claim 92 wherein the heat is provided by a sourceof hot air, such as a hair dryer, a hot air gun or a fan heater.
 94. Amethod of making a variable focus lens having a flexible, transparentmembrane supported in a frame, wherein the membrane is pre-tensioned,and the frame is mounted to the membrane while the membrane ispre-tensioned.
 95. Eyewear incorporating a variable focus lens asclaimed in claim 1, wherein said eyewear is in the form of sunglasses,swimming goggles, skiing goggles, squash glasses, sports eyewear ingeneral, welding masks, welding goggles, laboratory goggles, andprotective eyewear in general.
 96. Eyewear as claimed in claim 95,wherein said lens is provided as an insert.
 97. Eyewear as claimed inclaim 95, wherein the variable focus lens is attached to the outside ofthe eyewear.
 98. A variable focus lens comprising an envelope oftransparent fluid defined between two membranes, at least one of whichis flexible, wherein one or both of the membranes or the fluid istinted.
 99. A variable focus lens comprising an envelope of transparentfluid defined between two membranes, at least one of which is flexible,said flexible membrane being formed from metallized Mylar.